There is a volcano in Naples called Mt Vesuvius and it is really dangerous

It exploded in 79AD

When it erupted in 79AD the ash from the volcano hardened around the buildings (making a cocoon) which preserved them for along time and with people the ash harden around the people when they were about to die

If you want to find out when volcanoes are likely to erupt you can look at the patterns of when a volcano has erupted and then see the time patterns